The present invention relates to a sound insulating composite material used for automotive sound insulation and the like, and to a sound insulating cover member (made of the sound insulating composite material) disposed between automotive passenger compartment and engine compartment.
For example, an automotive steering shaft is equipped with a sound insulating cover member at a position between passenger compartment and engine compartment for the purpose of sound insulation and the like. In FIG. 4, a steering shaft 41 is passed through a through hole 43 of a dash panel 42 and connected to a steering box (not shown in the drawings). A sound insulating cover member 44 is formed on the steering shaft 41 for sealingly cover the through hole 43 for the purpose of sound insulation and preventing entry of dust and the like from an engine compartment 45 into a passenger compartment 46.
The sound insulating cover member 44 is required to have superior heat resistance and superior weather resistance since it is exposed to a high temperature atmosphere (particularly its engine compartment side) and to various weathers. Furthermore, it is required to have a good sound insulating property for providing a good habitability in the passenger compartment 46.
Japanese Patent Unexamined Publication JP-A-1-271444 discloses a sound insulating hole cover for covering a steering shaft hole between engine compartment and passenger compartment. This sound insulating hole cover is made of a composition containing 100 parts by weight of a polymer (EPM or EPDM) and 130-850 parts by weight of at least one inorganic filler selected from zinc flower, titanium oxide and barium sulfate. Due to this high content of the inorganic filler, the sound insulating hole cover may become insufficient in ordinary state properties (hardness, tensile strength and elasticity). Therefore, it may become difficult to fix the sound insulating hole cover to the dash panel using bolts or the like. Furthermore, the sound insulating hole cover may become inferior in sound insulation in a particular frequency range (e.g., about 500-1,200 Hz), since it tends to resonate to sound of engine compartment or the like due to the rubber elasticity property.
There is another conventional sound insulating cover member prepared by laminating together a first layer (made of a resin composition) and a second layer (made of a rubber composition). Although this cover member is capable of providing good ordinary state properties, the cost for producing the cover member is relatively high since the number of parts constituting this cover member becomes larger than other types of a single layer. Furthermore, it may become difficult to mount a laminate of the first and second layers at a proper position.
It is therefore an object of the present invention to provide a sound insulating composite material that is free from the above-mentioned problems.
It is another object of the present invention to provide a sound insulating composite material that is superior in ordinary state properties, sound insulation and heat resistance and does not resonate to sound of an automotive engine compartment or the like.
It is still another object of the present invention to provide a sound insulating cover member that is superior in mounting easiness, sound insulation, heat resistance and weather resistance.
It is a further object of the present invention to provide a process for producing the sound insulating composite material.
According to the present invention, there is provided a sound insulating composite material. This material comprises:
a crosslinked polymer containing 100 parts by weight of an ethylene-propylene rubber, 20-100 parts by weight of a polyethylene, and 100-200 parts by weight of a polypropylene, said crosslinked polymer being prepared by a dynamic crosslinking of said ethylene-propylene rubber with said polyethylene and said polypropylene in the presence of an organic peroxide; and
an inorganic filler in an amount of 200-500 parts by weight relative to 100 parts by weight of said ethylene-propylene rubber.
According to the present invention, there is provided a sound insulating cover member comprising said sound insulating composite material.
According to the present invention, there is provided a process for producing said sound insulating composite material. This process comprises:
(a) preparing a mixture containing said ethylene-propylene rubber, said polyethylene, said polypropylene, and said organic peroxide; and
(b) kneading said mixture while said mixture is in a melted condition, thereby generating said dynamic crosslinking.